For millions of people living in and around cities, the urban heat island effect, i.e., a metropolitan area which is significantly warmer than nearby rural areas, is of growing concern. The elevated temperatures associated with the heat island effect, as well as increasing global temperatures, are impacting communities by increasing peak energy demand, air conditioning costs, air pollution levels, and heat-related illness and mortality. In addition, as energy costs are rising, there is a need to reduce energy consumption. The use of “cool” materials in roads and building construction can be used to mitigate the heat island effect, reduce energy demand and energy consumption. The term “cool” materials is used to describe building materials that have high solar reflectance, or albedo, and which reflect a large portion of the sun's energy. Cool materials may also have a high thermal emittance, releasing a large percentage of absorbed heat.
Keeping building materials cooler in sunlight is historically known. For example, U.S. Pat. No. 21,927 dated Oct. 26, 1858 (Johnson) discloses a new composition for roofing which uses mica as a solar reflector material. Johnson claims: “The mica being transparent and reflective, will act as a reflector of the sun's rays and add greatly to the coolness of the building to which it is applied.” Other historical references also describe the use of building materials to ward off the sun's rays. See, e.g., U.S. Pat. Nos. 35,464; 2,133,988; 3,577,379; 4,289,677; 4,424,292; and 4,624,710. Other references describing pigments used to protect building materials from sun exposure are also known. See, e.g., U.S. Pat. No. 5,006,175. A color restoring (self-cleansing) concrete body based on photo-catalytic TiO2 in anatase form is described in U.S. Pat. No. 3,102,039.
Complex Inorganic Color Pigments (CICPs) that are IR reflective are disclosed in several U.S. Pat. Nos. 6,174,360, 6,416,868 and 6,541,112. These pigments are generally of spinel, rutile or corundum-hematite basic structure and are manufactured by several companies. Examples of these types of pigment are the Ferro's “GEODE® and Eclipse™ Cool Colors™”, The Shepherd Color Company's “Arctic® Colors”, BASF's (formerly Engelhard) “Meteor® and Meteor® Plus” and Heubach's “Heucodur®” CICP products. Other references are known which also describe coatings and pigments for use in building materials. See, e.g., U.S. patent application Ser. Nos. 10/680,693 and 10/746,829, which disclose the use of 2-part coatings with infrared reflective pigments primarily for use in coating roofing granules for asphalt roofing, such as shingles; and U.S. patent application Ser. No. 10/989,120, which discloses a thermally insulating reflective coating system which is comprised of infrared reflective pigments, hollow micro-spheres, various fillers and resins where the coating has insulating as well as reflective properties.
Work during the mid to late 1970's and early 1980's in ASTM established a standard for pigments used to integrally color concrete. See, e.g., ASTM Research Report, Pigments for Integrally Colored Concrete, Journal of Cement, Concrete and Aggregates (1980); ASTM C 979 Standard, Specification for Pigments for Integrally Colored Concrete, (1982). More recently, a European Standard EN 12878, Pigments for the colouring of building materials based on cement and/or lime, has been adopted by the European common market standards organization (CEN).
Interest in concrete as a means of improving albedo or SRI of pavement has been studied by Ting, Koomey and Pomerantz as well as by Levinson and Akbari, both groups from the Lawrence Berkeley National Laboratory, and also by Marceau and VanGeem of the Portland Cement Association. These studies have considered gray and white cements as the primary factor in the resulting albedo or solar reflectance of the concrete with supplementary cementitious materials (SCM's), contributing to the overall reflectivity. Marceau and VanGeem found that about 80% of the variation of solar reflectance of concrete was due to the cement reflectance when no SCM was present and 75% when SCM's were included and cement reflection was constant. They report that fine aggregates have a very small effect on the solar reflectance and that coarse aggregates also have been determined to play a very minor role in the resulting concrete's albedo or solar reflectance.
Concrete is a highly versatile and durable structural material that is widely used in nearly all modern construction. There has been a growing trend to make concrete more aesthetically pleasing and, more recently, to provide sustainable site development with concrete construction. However, colored (non-white) concrete that is suitable as a building material, and also having a high solar reflectance is not known. Therefore, there is a need for concrete and other cementitious systems and cementitious mixtures with improved properties to be used in cool hardscapes and building construction.